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Questions and Answers
What is the dimension of compressibility of a fluid?
What is the dimension of compressibility of a fluid?
What is the unit of dynamic viscosity in CGS system?
What is the unit of dynamic viscosity in CGS system?
What is the relation between dynamic viscosity and temperature in a liquid?
What is the relation between dynamic viscosity and temperature in a liquid?
What is the unit of kinematic viscosity in SI system?
What is the unit of kinematic viscosity in SI system?
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What is the property of a fluid that indicates resistance to flow over a surface?
What is the property of a fluid that indicates resistance to flow over a surface?
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What is the name of the instrument used to measure dynamic viscosity?
What is the name of the instrument used to measure dynamic viscosity?
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What is the definition of ideal fluid?
What is the definition of ideal fluid?
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What is the unit of bulk modulus?
What is the unit of bulk modulus?
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What is the density of mercury?
What is the density of mercury?
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What is the dimension of specific weight?
What is the dimension of specific weight?
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What is the specific gravity of water at 4°C?
What is the specific gravity of water at 4°C?
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What is the device used to measure specific gravity of a liquid?
What is the device used to measure specific gravity of a liquid?
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What is compressibility?
What is compressibility?
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What is the temperature at which water assumes its maximum density?
What is the temperature at which water assumes its maximum density?
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What is the expression for bulk modulus for an adiabatic process?
What is the expression for bulk modulus for an adiabatic process?
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What is the relationship between the surface tension of mercury and water at normal temperature?
What is the relationship between the surface tension of mercury and water at normal temperature?
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What happens to the surface tension of water when the temperature decreases?
What happens to the surface tension of water when the temperature decreases?
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What is the condition for the liquid level to rise in a glass tube?
What is the condition for the liquid level to rise in a glass tube?
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What is the characteristic of the wetting phenomenon?
What is the characteristic of the wetting phenomenon?
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What is the formula for the height of liquid in a capillary tube?
What is the formula for the height of liquid in a capillary tube?
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What is the condition for the non-wetting phenomenon?
What is the condition for the non-wetting phenomenon?
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What is the primary characteristic of an ideal fluid?
What is the primary characteristic of an ideal fluid?
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Which of the following fluids does not follow Newton's law of viscosity?
Which of the following fluids does not follow Newton's law of viscosity?
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What is the relation between shear stress and velocity gradient in a time-independent non-Newtonian fluid?
What is the relation between shear stress and velocity gradient in a time-independent non-Newtonian fluid?
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Which of the following fluids has an apparent viscosity that is a function of time?
Which of the following fluids has an apparent viscosity that is a function of time?
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What is the primary reason for the existence of surface tension in a fluid?
What is the primary reason for the existence of surface tension in a fluid?
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Why do liquid droplets take the spherical shape?
Why do liquid droplets take the spherical shape?
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Which of the following fluids is a Bingham plastic fluid?
Which of the following fluids is a Bingham plastic fluid?
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What is the gauge pressure inside a spherical drop?
What is the gauge pressure inside a spherical drop?
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Study Notes
Fluid Properties
- Density (ρ) is a measure of mass per volume, with units of kg/m³.
- Example densities: ρair = 1.2 kg/m³, ρwater = 1000 kg/m³, ρHg = 13600 kg/m³.
Specific Weight or Weight Density
- Specific weight represents the force exerted by gravity on unit volume of a fluid.
- It can be used as a characteristic property of a fluid.
- Dimension of Specific Weight = M¹L⁻²T⁻².
Specific Gravity
- Specific gravity is used to define the density of a liquid as compared to the density of an equal volume of water at a specified temperature.
- The temperature used for measurement is usually 4°C, because this temperature allows water to assume its maximum density.
- Specific gravity is a function of temperature.
- Specific gravity of water is 1 at 4°C.
- Hydrometer is used to measure the specific gravity of a liquid.
Bulk Modulus
- Bulk modulus is defined as the ratio of the infinitesimal pressure increase to the resulting decrease of the volume.
- It is a measure of resistance to compressibility of a fluid.
- Unit of Bulk Modulus = N/m² or Pa.
- Dimension of Bulk Modulus = M¹L⁻¹T⁻².
Compressibility (β)
- Compressibility is a measure of the relative volume change of a fluid or solid as a response to pressure change.
- It is the reciprocal of bulk modulus.
- Unit of Compressibility = Pa⁻¹.
- Dimensions of Compressibility = M⁻¹L¹T².
Viscosity
- Viscosity is the property of a fluid that indicates resistance to flow over a surface.
- In case of liquids, viscosity is due to cohesion forces, and in case of gases, viscosity is due to molecular momentum transfer.
- Kinematic viscosity: S.I. unit = m²/s, C.G.S unit = cm²/s = Stoke.
- Dynamic viscosity (μ) or absolute viscosity: S.I. unit = kg/m-s = Pa – s, C.G.S unit = Poise.
- Dimension of Dynamic viscosity (μ) = M¹L⁻¹T⁻¹.
- Dimension of Kinematic viscosity (ν) = M⁰L²T⁻¹.
- Redwood viscometer is used to measure Dynamic viscosity or absolute value of viscosity.
Effect of Temperature and Pressure on Viscosity
- For liquids:
- If temperature increases: μ and ν decreases.
- If pressure increases: μ and ν remains same.
- For gases:
- If temperature increases: μ and ν increases.
- If pressure increases: μ remains same and ν decreases.
Types of Fluid
- Ideal Fluid:
- Viscosity is zero, meaning resistance to shearing deformation is zero.
- No shear stress in the case of an ideal fluid.
- An ideal fluid is frictionless and incompressible.
- An ideal fluid has negligible surface tension.
- Newtonian fluid:
- Follows Newton’s law of viscosity.
- Examples: water, alcohol, gasoline.
- Non-Newtonian fluid:
- Does not follow Newton’s law of viscosity.
- Relation between shear stress and velocity gradient is given as:
- Time Independent Non-Newtonian fluid:
- Apparent viscosity is not a function of time.
- Examples: honey, quick sand, starch solution.
- Time dependent Non-Newtonian Fluid:
- Apparent viscosity is a function of time.
- Examples: Ketchup, paints, sludgy.
Surface Tension
- Surface Tension is the property of a fluid that tries to shrink the fluid into the minimum surface area.
- It exists due to the intermolecular force of attraction (Cohesive force) between the molecules of same fluid.
- Gauge pressure inside a spherical drop, bubble, and liquid jet.
- Due to surface tension only, liquid droplets take the spherical shape because the spherical shape has the smallest surface area for a given volume.
Wetting and Non-Wetting Phenomenon
- Wetting phenomenon:
- Adhesive force > cohesive force.
- Angle of contact is less than π/2.
- Non-wetting phenomenon:
- Adhesive force < cohesive force.
- Angle of contact is more than π/2.
Capillary
- Height of liquid in capillary tube is given by:
- Where, σ is surface tension of liquid and tube, θ is angle of contact, and d is diameter of capillary tube.
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Description
Basic properties of fluids, including density and specific weight, in the context of fluid mechanics.
